Week 17 in the NFL didn't look like much going in. Resting stars, chilly temperatures, plenty of teams with nothing on the line. Much of the focus already had turned to what came after -- coach firings and hirings. Yeah, as of a couple of days ago, you wouldn't have expected much for a post-Week 17 column about what we learned.

So what did we learn at the end of that late Sunday game window? Glad you asked:

Ninety-seven percent is not 100 percent

Entering the day, ESPN's Football Power Index rated the Ravens' chances of making the playoffs at 97 percent. All they had to do was beat the Bengals at home, and even if they didn't do that, all they needed was for the Titans to lose to the Jaguars or the Bills to lose in Miami. Ravens fans slipped into their old Ray Lewis jerseys Sunday morning with a high degree of confidence. I mean, 97 percent, right?

And here's the final AFC wild card plot, from after the Bills' win was complete, of an insane late afternoon window.

Seth Walder, ESPN Analytics

Not so much. See, while the proliferation of calculated win probabilities as part of football analysis can be helpful and make for cool-looking graphs (like the wild one above), it also can lead to fan complacency. That 97 percent is a comforting number, but what it means is that, three times out of a hundred, the outcome is not the one it appears to ensure. Three times out of a hundred isn't impossible. It's not even all that crazy. By rights, the Ravens should have been fine Sunday. But that ball isn't round, and sometimes it bounces funny.

The stunning turnaround at the end of the Bengals-Ravens game, as Bills players and the city of Buffalo watched with what they well knew was the slimmest of hope, is a reminder of why we watch these games. Sports are at their best not when they confirm our expectations, but when they reset them. We watch these games to be dazzled, and Andy Dalton's 49-yard touchdown pass to Tyler Boyd on fourth-and-12 with 44 seconds left in the season was the "oh my God" moment of Week 17.

If somebody had told you right before that play that there was a 3 percent chance the Bengals were scoring, you'd have thought their estimate high. But you had to watch, just in case. That play, that moment, were the answer to, "In case of what?" If you're a Bills fan, it was the best kind of unexpected joy. If you were a Ravens fan, it was that familiar kind of sports-inflicted pain. If you didn't care who won but were just watching to see something amazing, you got your reward.

It doesn't happen all the time, which is what makes it so great when it does. Sports are at their best when they remind us we don't know what to expect. Remember next year, if your team enters Week 17 with a 13 percent chance of making the playoffs as the Bills did Sunday: As long as that percentage is above zero, it's worth watching. Just in case.

NFL parity is alive and well

Of the 12 playoff teams this year, eight were not in the playoffs last year, including all four NFC division winners. According to the Elias Sports Bureau, that ties for the most new playoff teams from one season to the next since the NFL went to a 12-team playoff format in 1990 (there were also eight new playoff teams in 2003). It's the first time since the league expanded to eight divisions in 2002 that one conference had four division champions that weren't playoff teams the year before.

And this isn't a parity-means-mediocrity issue, either. Five of the six NFC playoff teams won at least 11 games, and the sixth was last year's conference champion. These are high-quality teams and a field from which it's tough to predict a winner. (I think I'm taking the New Orleans Saints, for example, but their first game is against a team they already beat twice, and it's hard to beat the same team three times, so how the heck do I know?)

Super Bowl LII Coverage

The Eagles upset the Patriots to secure their first Super Bowl victory.

What does it all mean? Well, for better or for worse, this is the flip side of one of the league's biggest 2017 problems -- namely, so many stars getting hurt and suspended. Would the playoff field have looked different if not for injuries to Aaron Rodgers, Odell Beckham Jr., Andrew Luck, J.J. Watt, Deshaun Watson, Richard Sherman and Kam Chancellor? Could the Cowboys have mounted a better NFC East title defense if Ezekiel Elliott hadn't been suspended six games? Unanswerable questions, but the fact is that those players all play for teams that made the playoffs last year and didn't this year.

The silver lining is the fresh faces who step in to take those players' places in the spotlight. This year's NFC playoffs will feature the Saints' young running back tandem and secondary, Panthers star running back Christian McCaffrey, the Rams' brilliant Aaron Donald and Todd Gurley. Sadly, they won't feature Philadelphia's brilliant but injured quarterback Carson Wentz, but the season certainly offered him a showcase. In the AFC, new participants include Marcus Mariota, Leonard Fournette, Tyrod Taylor and maybe LeSean McCoy, if he's healthy.

We'd rather see the megastars all playing, but the nature of football is that there will be injuries. Part of the residue of that is the week-to-week, year-to-year unpredictability of it all, and the drama that comes with it.

Four months ago, if I'd told you Todd Bowles was safe in New York and Jack Del Rio was out in Oakland, you'd have thought I was nuts. Same thing if, four weeks ago, I'd told you Dirk Koetter was safe in Tampa Bay and Jim Caldwell was out in Detroit. We try to forecast these things, and in doing so, we apply the input we get from people inside the game who are plugged into these situations. But the truth is even those people often don't know what the owners are going to do when it's all said and done. Sometimes, owners change their minds, and the thing everybody was sure would happen ... doesn't.

Heck, look at Cleveland, where one of the most famously impatient owners in the league said he's sticking with a coach who didn't win a game all year and won only one the year before. Job security for 1-31 Hue Jackson is the ultimate symbol of the mercurial nature of coaching decisions made at an ownership level. Jimmy Haslam has jettisoned coaches with significantly better records than Jackson's.

Sometimes, you can see these things coming. We all expected the Bears and Colts to make changes, and they are. But more often than not, we don't know exactly what a team owner is thinking until he or she makes a move. And sometimes, even if we do know what the billionaires in charge of the decisions are thinking, they change their minds at the last second.

Guide To NFL Coaching Carousel

Part of the problem is that it's hard to find good head coaches, and most of the ones hired in this cycle aren't going to work out. Everybody wants to find the next Sean McVay, but it's more possible than not that there is no McVay in this year's field of candidates. (And by the way, I get why everyone wants to find the next McVay, but didn't Jacksonville go in the exact opposite direction and win only one fewer game than the Rams? Why aren't teams trying to find the next old-school Tom Coughlin/Doug Marrone combo to design a boot-camp-style training camp and whip their sorry groups into shape?)

It's tough to find the right guy, but teams could do a better job of helping their chances to succeed. For instance, I disagree with the separation-of-powers Giants hiring the general manager before the coach. And I kind of disagree with the Bears firing the coach and extending the GM. I think the coach is the more important hire, and if you're doing this, you need to make sure the coach-GM combo is in lockstep and that the coach is OK with the GM. San Francisco did this last offseason. Buffalo kind of did, too, though it took a little longer to sort it all out. Would the Giants be in a better situation now if they'd changed the coach and GM together two years ago instead of just one?

Regardless, I'll repeat my annual sermon here about coaches. You'll hear a lot about "defensive-minded" and "offensive-minded" head coaches, and which your team needs. It's baloney. What your team needs, no matter which team we're talking about, is a leader of men. An NFL head coach has to be someone who can communicate and implement his vision for how to win games, who can assess his roster and figure out a way to win with it (not turn it over to bring in only players who "fit his system"). Offense, defense, whatever ... this is the head coach. It's not easy, but it's essential.